IL-15, AN IMMUNOMODULATOR OF T-CELL RESPONSES IN INTRACELLULAR INFECTION

IL-15 is a novel cytokine with potent T cell growth factor activity. H ere, we investigated the role of IL-15 in the human immune response to intracellular infection by studying patients leprosy. We found that I L-15 mRNA and protein were more strongly expressed in immunologically resistant tuberculoid patients than in with unresponsive and susceptib le lepromatous patients. In vitro, Mycobacterium leprae induced IL-15 secretion from peripheral blood monocytes. Furthermore, rIL-15 by itse lf and in combination with rIL-2 or rlL-7 augmented PBMC proliferative responses to the pathogen. Although rIL-15 expanded the CD3(-)CD56(+) (NK) subset, rIL-15 combined with M. leprae induced the expansion of CD3(+)CD56(+) T cells. Immunohistologic analysis of leprosy skin lesio ns indicated that the frequency of CD56(+) cells was greatest in the g roup of patients with high IL-15 expression, and that >90% of the CD56 (+) cells in lesions were CD3(+) T cells. Therefore, IL-15 augments th e local T cell response to human intracellular pathogen.